Name: sonic testing of concrete beams
Uploaded: 2024-11-07T14:48:41.000Z
Duration: 1 min 16 s
Channel: JoVE

Stress analysis in concrete structures prone to dynamic and impact loading employs the dynamic modulus, which is greater than the static modulus of elasticity of the concrete.
The dynamic modulus of elasticity is determined using a sonic test where a concrete beam of standard dimensions is prepared and clamped at its center. 
One end of the beam is connected to an electromagnetic exciter unit designed to initiate vibrations, while the other end is connected to a pick-up for detecting these vibrations, which are then amplified and measured using an indicator.
The beam resonates at the fundamental frequency and is verified by the maximum deflection recorded in the indicator.
The value of the fundamental frequency, along with the values of the beam&#39;s length and density, is used to compute the concrete specimen&#39;s dynamic modulus of elasticity.
Alternatively, from the stress-strain curve of concrete, the initial tangent modulus is determined by drawing a tangent at the curve&#39;s origin and calculating its slope, which gives an approximate value of the dynamic modulus of elasticity of the concrete specimen.

dynamic modulus of elasticity of concrete

Dynamic Modulus of Elasticity of Concrete

The dynamic modulus of elasticity assesses how a concrete structure deforms under impact or dynamic loads. It is typically higher than the static modulus of elasticity, measured under slow, steady loading conditions.
The sonic test is a common method to determine the dynamic modulus. In this test, a concrete beam, sized either 6 x 6 x 30 inches or 4 x 4 x 20 inches, is clamped at its center. Vibrations are initiated at one end of the beam by an electromagnetic exciter unit powered by a variable-frequency oscillator. A pick-up device at the other end detects these vibrations, which are then amplified and measured using an indicator.
The vibrations at varying frequencies are transmitted through the specimen till it starts to resonate at its fundamental frequency. The dynamic modulus of elasticity (Ed) in pounds per inch is computed mathematically by substituting the beam's fundamental frequency (n) in Hertz, length (L) in inches and density (&#9076;) in pounds per cubic feet.
<img alt="Equation for depolarization energy, \(E_d=6n^2L^2\rho \times 10^{-6}\), related to optical properties." src="/files/ftp_upload/16926/16926_PT_Equation_001.svg" style="height: 15px;" data-altupdatedat="1762173717000" data-alt="Eq1" />
Another method to estimate the dynamic modulus involves the stress-strain curve of concrete. By drawing a tangent at the curve's origin and calculating its slope, the initial tangent modulus is determined. This value is approximately equal to the dynamic modulus of elasticity.
<img alt="Dynamic modulus of elasticity, stress-strain graph, tangent elasticity, material deformation analysis." src="/files/ftp_upload/16926/16926_PT_Figure_001.jpg" data-altupdatedat="1762173717000" data-alt="Figure 1" />

Stress analysis in concrete structures prone to dynamic and impact loading employs the dynamic modulus, which is greater than the static modulus of ...

dynamic-modulus-of-elasticity-of-concrete

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Civil Engineering

Unit 1

Elasticity, Creep, and Shrinkage in Concrete

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KEY TERMS AND CONCEPTS

sonic testing of concrete beams

Sonic testing of concrete beams is used to measure the dynamic modulus of elasticity. This value describes how a concrete specimen deforms under impact or other dynamic loads. It is usually higher than the static modulus of elasticity, which is measured under slow, steady loading.

A common test uses a concrete beam that is either 6 x 6 x 30 inches or 4 x 4 x 20 inches. The beam is clamped at its center. Vibrations start at one end with an electromagnetic exciter unit powered by a variable-frequency oscillator.

A pick-up device at the other end detects the vibrations. The signal is amplified and read with an indicator. The test continues through changing frequencies until the specimen resonates at its fundamental frequency.

The dynamic modulus of elasticity, Ed, is then calculated from the beam’s fundamental frequency, length, and density. The frequency is measured in Hertz, length in inches, and density in pounds per cubic feet. Another way to estimate the dynamic modulus is from the stress-strain curve of concrete.

For that method, a tangent is drawn at the origin of the curve. The slope of this line gives the initial tangent modulus. This value is approximately equal to the dynamic modulus of elasticity.

Sonic Testing of Concrete Beams

elasticity in concrete

Concrete Stress-Strain Modulus Methods

Concrete shows a non-linear stress-strain response when it is loaded in uniaxial compression or tension at moderate to high stress levels. As the load is removed, the stress-strain path does not return along the same line. This creates a hysteresis loop and shows that concrete is not perfectly elastic. The modulus of elasticity is used to describe stiffness. In many materials, it is taken from the slope of the linear part of the stress-strain curve. Concrete does not have a simple linear...

Sonic testing of concrete beams is used to measure the dynamic modulus of elasticity. This value describes how a concrete specimen deforms under impact or other dynamic loads. It is usually higher than the static modulus of elasticity, which is measured under slow, steady loading. A common test uses a concrete beam that is either 6 x 6 x 30 inches or 4 x 4 x 20 inches. The beam is clamped at its center. Vibrations start at one end with an electromagnetic exciter unit powered by a...

creep in concrete

Concrete Creep Under Constant Load

Concrete creep is the time-dependent increase in strain under a sustained load. It is different from shrinkage, swelling, and thermal expansion, which are other time-based changes in concrete. When concrete stays under constant stress, its shape can slowly change over time. The main cause of creep is the loss of physically adsorbed water from calcium silicate hydrate in the hydrated cement paste. Concrete also shows a non-linear stress-strain relationship, which adds to this behavior.

factors affecting creep

Concrete Creep: How Material Choices Matter

Concrete creep depends on the materials in the mix, the load applied, and the curing environment. In normal-weight aggregate concrete, the hardened cement paste is the main part that creeps. The aggregates are stiffer than the cement paste, so they resist stress-induced deformation more effectively. Aggregate properties can change how much a concrete member creeps. The stiffness of the aggregates is described by their modulus of elasticity. When aggregates make up a larger volume of the...

effects of creep

Creep in Concrete Structures

Creep in concrete is the slow deformation that happens when a load stays on a structure for a long time. It can change how beams, columns, bridges, and other concrete members behave over time. Engineers must account for it when they design safe and durable structures. In reinforced concrete beams, creep increases deflection, which means the beam bends more than expected. That extra bending can widen cracks and may require added design measures. In slender columns under eccentric loads, creep...

shrinkage in concrete

Concrete Shrinkage and Crack Risk

Concrete shrinkage is the loss of volume that happens when water leaves the mix or when cement reacts and carbonates. This contraction creates volumetric strain in the material. In practice, engineers often measure shrinkage as linear strain, which is about one-third of the volumetric strain. Fresh concrete can also shrink while it is still plastic. This plastic shrinkage can reduce the volume by about 1% of the concrete’s absolute volume. It usually happens when water evaporates from the...

drying shrinkage

Concrete Shrinkage as Water Evaporates

Concrete shrinkage happens when hardened concrete loses water to air with a relative humidity below 100 percent. Free water in the capillaries evaporates first. Then water that was adsorbed, or held on the calcium silicate hydrates, moves into these empty spaces and evaporates too. As more water leaves, the concrete volume decreases. This is called drying shrinkage. Some of this change can be reversed. If the concrete later meets moisture, it can take in water again and expand slightly. Not...

carbonation shrinkage

Concrete Carbonation and Steel Corrosion

Concrete carbonation begins when atmospheric carbon dioxide enters the pores of concrete. If moisture is present, the gas forms carbonic acid. That acid reacts with calcium hydroxide in hydrated cement and produces calcium carbonate. This reaction causes carbonation shrinkage, which means the concrete loses some volume. The calcium carbonate can also fill pores, so permeability drops slightly. At the same time, the water released during the reaction can help any unreacted cement continue...

types of non-structural cracks in concrete

types-of-non-structural-cracks-in-concrete

Concrete Cracks from Shrinkage and Heat

Non-structural concrete cracks can form during placement, curing, and drying. The main groups are plastic cracks, early-age thermal cracks, and drying shrinkage cracks. Another surface pattern called crazing can also appear when finishing or curing is not done well. Plastic cracks form while the concrete is still fresh. Plastic shrinkage cracks usually appear within hours after pouring. The top of the concrete dries faster than the lower part, which creates tensile stress. The soft concrete...

mass concreting

Preventing Thermal Cracks in Large Concrete

Large concrete pours can build up heat and crack as they cool. This is a key challenge in mass concreting, such as the placement of concrete in gravity dams. Heat from cement hydration, which is the chemical reaction that hardens cement, can create a temperature difference between the inside and outside of the concrete mass. That temperature gradient may lead to thermal cracks. To lower that risk, the concrete mix is adjusted before placement. Low-heat cement and pozzolans are used to reduce...

hot weather concreting

Managing Heat in Concrete Placement

Hot weather changes how concrete sets and cures. High temperatures speed up hydration, which makes the mix set faster. That faster set can lower the long-term strength of the finished structure. Low air humidity creates another problem. Water leaves the fresh concrete more quickly, so workability drops. This can also increase plastic shrinkage, which is shrinkage before the concrete hardens, and raise the chance of crazing, a network of fine surface cracks. Several simple steps can reduce...

cold weather concreting

Preventing Freeze Damage in Fresh Concrete

Fresh concrete can be damaged if it freezes before it sets. When the water in the mix turns to ice, it expands. That expansion disrupts setting, slows the chemical reactions needed for hardening, and can leave more pores in the finished concrete. Those extra pores weaken the final structure. If the concrete gains enough strength before freezing, the damage may be reduced. Cold-weather protection focuses on keeping the concrete warm during and after placement. Mixing with warm water and heated...

key terms and concepts

Learn how sonic testing measures the dynamic modulus of elasticity in concrete beams, from resonance and vibration detection to calculation and tangent modulus.

Sonic Testing of Concrete Beams | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

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Sonic Testing of Concrete Beams

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